Antibiotics are our first line of defense against bacterial pathogens that have historically been a plague on human civilization. Increasingly, human pathogens that had been regarded as treatable infectious agents are becoming serious problems as a result of antibiotic resistance. There is an urgent need for novel antibiotics in the pharmaceutical pipeline, yet for many reasons the pharmaceutical industry has not invested heavily in the antibiotic discovery process. The best possible resource for antibiotic discovery is to explore microbial communities, where complex chemistries have naturally evolved. To access the complex chemistries from diverse microorganisms, this proposal uses a community genomic approach in which biosynthetic genes from diverse microorganisms are directly recovered from soils and expressed in E. coli or other bacterial hosts. A collection of fourty-four clones that produce antibiotic activity has already been isolated from these community genomic libraries. The proposed research will determine the chemical structure of antibiotic compounds from this collection, and determine the potency and any toxicity associated with these compounds. In addition to clones that express antibiotic activity, another collection of clones has been isolated that contain the genes for a specific class of natural product, the polyketides. Polyketide compounds have diverse structures, and diverse activities, such as antimicrobial and anticancer properties. A genetic analysis of polyketide biosynthesis pathways discovered from a soil microbial community library indicates that the 34 polyketide-containing clones are very different from known polyketide pathways. Our research efforts will transfer these polyketide pathways into a novel cloning vector, designed to allow transfer of genetic pathways between Gram-negative bacteria, and then genetic and bioassay screens will determine whether these polyketide pathways are expressed in different bacterial species. The results of this research will be a collection of lead candidate compounds with antimicrobial activity, novel polyketide biosynthetic pathways useful in engineering novel polyketide structures with therapeutic properties, an evaluation of a novel Gram- negative shuttle vector, and the next generation of microbial community genomic library for future development of this technology. PUBLIC HEALTH RELEVANCE: Antibiotics are critical to our ability to combat infectious disease, and especially in an era in which the incidence of antibiotic resistance is on the rise there is a need for discovery and development of clinically useful antibiotics. Using new technology for cloning and expressing genetic pathways from diverse microorganisms, a collection of clones that either produce an antimicrobial activity or encode a biosynthetic pathway have been isolated. The proposed research would evaluate this collection of clones at a genetic and biochemical level to determine which lead candidates have the best potential as novel therapeutic agents.